This article is a fan-based attempt to give an overview of the cosmology of J.R.R. Tolkien's fictional Arda universe. Tolkien gave several important clues as to the shape and nature of his universe, but there are also several important gaps he left unfilled. This article hopefully will fill them a bit better.
The Flat Arda Edit
When Illuvatar created Ea, the universe, he made it with apparently geocentric design; the flat world of Arda was at the center, the space containing stars and planets ringed around it, and Illuvatar's heavenly realm on the outside. The sun and moon each circled around the world once a day, going over the land and then underneath the ground.